The reaction of dicarboxylic acids in a non-aqueous medium by the so-called "pyridine process" is known (DT-OS (German Published Specification) No. 1,495,912, U.S. Pat. No. 3,030,331, DT-OS (German Published Specification) No. 1,420,476 and U.S. Pat. No. 3,220,976).
The reaction of dicarboxylic acids by the so-called "transesterification process" is also known (DT-OS (German Published Specification) No. 1,420,475, U.S. Pat. No. 3,169,121 and U.S. Pat. No. 3,207,814).
The reaction of dicarboxylic acids by the so-called "suspension process" using inert organic liquids is also known (DT-OS (German Published Specification) No. 1,495,906 and U.S. Pat. No. 3,290,409).
The reaction of dicarboxylic acid halides by the two-phase boundary process is also known (U.S. Pat. No. 3,207,814, column 6, lines 60 to 65).
All of these process variants for incorporating ester groupings in polycarbonates have disadvantages either because of the process conditions or because of the properties of the polyester-carbonates obtainable by these processes.